IEEE Power & Energy Magazine - November/December 2015 - 52

Ensemble Methods and Blending of Forecasts

Sky Imagers

Numerical Weather Prediction
with Model Output Statistics

Climatology

Satellite Imagery

Statistical Learning Methods

1

2

3
4
5
6
Time Horizon for Which Method Shows Value (Hours)

120

240

figure 1. An overview of solar forecasting methods, based on time horizon for which they show value.

motion. Clouds scatter some wavelengths of light more than
they do others, and these can be used to categorize clouds as
thick and thin as well as to differentiate them from aerosols
or dust. Consecutive images can estimate cloud velocity and
so can provide a very short-horizon forecast. If additional sky
imagers are available, triangulation can provide information on
cloud base and depth as well as differential advection speed at
different cloud levels. Sky imagers are of significantly decreasing value beyond approximately a 30-min time frame; moreover, they are expensive to use relative to most other forms of
very short-term prediction.

Satellite Imaging
Providing value for a longer look-ahead time frame, geostationary satellite data from networks such as the National
Oceanic and Atmospheric Administration (NOAA) Geostationary Operational Environmental Satellite network for
North and South America and the MeteoSat network for
Europe, Africa, and central Asia supply information about
cloud properties and movement. First, a physically driven
model predicts clear-sky conditions at a specific site, using
inputs like aerosol content, water vapor, elevation, and ozone.
This modeled clear-sky irradiance is then modulated by estimated irradiance derived from satellite images. Sequential
satellite images are combined to create cloud motion vector fields that can be used to predict future cloud locations.
This technique has been shown to be effective in forecasting
irradiance from one minute to as far as five hours ahead.
However, it performs less effectively during conditions when
clouds are rapidly forming or dissipating, such as convective
and marine layer cloud regimes.
52

ieee power & energy magazine

Numerical Weather Prediction
NWP systems have been the workhorse of forecasting
applications for many years. Traditionally, these have performed best for the time horizon from six hours to two
weeks; recently deployed rapid-update systems (such as
the NOAA High-Resolution Rapid Refresh system) can
provide value at shorter time scales. NWP methods have
been well described in previous articles in relation to
wind. These involve solving the Navier-Stokes equations to
model the weather, combined with modules that compute
other physical processes, such as radiative transfer, land
surface effects, and cloud microphysics parameterization.
Historically, these models have been optimized for predicting variables such as temperature, humidity, probability
of precipitation, and wind. Only recently has there been an
emphasis on improving prediction of surface solar irradiance.
Statistical learning methods are often used to correct for errors
in the NWP model output and to blend output from multiple
models in a process referred to as model output statistics. It is
typical for such methods to improve upon the raw forecast of
an NWP model by about 10-15%.

Ensemble Forecasting
Ensemble methods are important to deal with the uncertainty inherent to solar power forecasting, particularly during morning and evening ramps and with cloud cover and
fog. An ensemble consists of a collection of forecasts and
can represent the uncertainty in the calculation of the state of
the atmosphere inherent in forecasting methods. Two major
techniques are employed in creating an ensemble: the first
adds perturbations to the initial state of a forecasting model,
november/december 2015



Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2015

IEEE Power & Energy Magazine - November/December 2015 - Cover1
IEEE Power & Energy Magazine - November/December 2015 - Cover2
IEEE Power & Energy Magazine - November/December 2015 - 1
IEEE Power & Energy Magazine - November/December 2015 - 2
IEEE Power & Energy Magazine - November/December 2015 - 3
IEEE Power & Energy Magazine - November/December 2015 - 4
IEEE Power & Energy Magazine - November/December 2015 - 5
IEEE Power & Energy Magazine - November/December 2015 - 6
IEEE Power & Energy Magazine - November/December 2015 - 7
IEEE Power & Energy Magazine - November/December 2015 - 8
IEEE Power & Energy Magazine - November/December 2015 - 9
IEEE Power & Energy Magazine - November/December 2015 - 10
IEEE Power & Energy Magazine - November/December 2015 - 11
IEEE Power & Energy Magazine - November/December 2015 - 12
IEEE Power & Energy Magazine - November/December 2015 - 13
IEEE Power & Energy Magazine - November/December 2015 - 14
IEEE Power & Energy Magazine - November/December 2015 - 15
IEEE Power & Energy Magazine - November/December 2015 - 16
IEEE Power & Energy Magazine - November/December 2015 - 17
IEEE Power & Energy Magazine - November/December 2015 - 18
IEEE Power & Energy Magazine - November/December 2015 - 19
IEEE Power & Energy Magazine - November/December 2015 - 20
IEEE Power & Energy Magazine - November/December 2015 - 21
IEEE Power & Energy Magazine - November/December 2015 - 22
IEEE Power & Energy Magazine - November/December 2015 - 23
IEEE Power & Energy Magazine - November/December 2015 - 24
IEEE Power & Energy Magazine - November/December 2015 - 25
IEEE Power & Energy Magazine - November/December 2015 - 26
IEEE Power & Energy Magazine - November/December 2015 - 27
IEEE Power & Energy Magazine - November/December 2015 - 28
IEEE Power & Energy Magazine - November/December 2015 - 29
IEEE Power & Energy Magazine - November/December 2015 - 30
IEEE Power & Energy Magazine - November/December 2015 - 31
IEEE Power & Energy Magazine - November/December 2015 - 32
IEEE Power & Energy Magazine - November/December 2015 - 33
IEEE Power & Energy Magazine - November/December 2015 - 34
IEEE Power & Energy Magazine - November/December 2015 - 35
IEEE Power & Energy Magazine - November/December 2015 - 36
IEEE Power & Energy Magazine - November/December 2015 - 37
IEEE Power & Energy Magazine - November/December 2015 - 38
IEEE Power & Energy Magazine - November/December 2015 - 39
IEEE Power & Energy Magazine - November/December 2015 - 40
IEEE Power & Energy Magazine - November/December 2015 - 41
IEEE Power & Energy Magazine - November/December 2015 - 42
IEEE Power & Energy Magazine - November/December 2015 - 43
IEEE Power & Energy Magazine - November/December 2015 - 44
IEEE Power & Energy Magazine - November/December 2015 - 45
IEEE Power & Energy Magazine - November/December 2015 - 46
IEEE Power & Energy Magazine - November/December 2015 - 47
IEEE Power & Energy Magazine - November/December 2015 - 48
IEEE Power & Energy Magazine - November/December 2015 - 49
IEEE Power & Energy Magazine - November/December 2015 - 50
IEEE Power & Energy Magazine - November/December 2015 - 51
IEEE Power & Energy Magazine - November/December 2015 - 52
IEEE Power & Energy Magazine - November/December 2015 - 53
IEEE Power & Energy Magazine - November/December 2015 - 54
IEEE Power & Energy Magazine - November/December 2015 - 55
IEEE Power & Energy Magazine - November/December 2015 - 56
IEEE Power & Energy Magazine - November/December 2015 - 57
IEEE Power & Energy Magazine - November/December 2015 - 58
IEEE Power & Energy Magazine - November/December 2015 - 59
IEEE Power & Energy Magazine - November/December 2015 - 60
IEEE Power & Energy Magazine - November/December 2015 - 61
IEEE Power & Energy Magazine - November/December 2015 - 62
IEEE Power & Energy Magazine - November/December 2015 - 63
IEEE Power & Energy Magazine - November/December 2015 - 64
IEEE Power & Energy Magazine - November/December 2015 - 65
IEEE Power & Energy Magazine - November/December 2015 - 66
IEEE Power & Energy Magazine - November/December 2015 - 67
IEEE Power & Energy Magazine - November/December 2015 - 68
IEEE Power & Energy Magazine - November/December 2015 - 69
IEEE Power & Energy Magazine - November/December 2015 - 70
IEEE Power & Energy Magazine - November/December 2015 - 71
IEEE Power & Energy Magazine - November/December 2015 - 72
IEEE Power & Energy Magazine - November/December 2015 - 73
IEEE Power & Energy Magazine - November/December 2015 - 74
IEEE Power & Energy Magazine - November/December 2015 - 75
IEEE Power & Energy Magazine - November/December 2015 - 76
IEEE Power & Energy Magazine - November/December 2015 - 77
IEEE Power & Energy Magazine - November/December 2015 - 78
IEEE Power & Energy Magazine - November/December 2015 - 79
IEEE Power & Energy Magazine - November/December 2015 - 80
IEEE Power & Energy Magazine - November/December 2015 - 81
IEEE Power & Energy Magazine - November/December 2015 - 82
IEEE Power & Energy Magazine - November/December 2015 - 83
IEEE Power & Energy Magazine - November/December 2015 - 84
IEEE Power & Energy Magazine - November/December 2015 - 85
IEEE Power & Energy Magazine - November/December 2015 - 86
IEEE Power & Energy Magazine - November/December 2015 - 87
IEEE Power & Energy Magazine - November/December 2015 - 88
IEEE Power & Energy Magazine - November/December 2015 - 89
IEEE Power & Energy Magazine - November/December 2015 - 90
IEEE Power & Energy Magazine - November/December 2015 - 91
IEEE Power & Energy Magazine - November/December 2015 - 92
IEEE Power & Energy Magazine - November/December 2015 - 93
IEEE Power & Energy Magazine - November/December 2015 - 94
IEEE Power & Energy Magazine - November/December 2015 - 95
IEEE Power & Energy Magazine - November/December 2015 - 96
IEEE Power & Energy Magazine - November/December 2015 - 97
IEEE Power & Energy Magazine - November/December 2015 - 98
IEEE Power & Energy Magazine - November/December 2015 - 99
IEEE Power & Energy Magazine - November/December 2015 - 100
IEEE Power & Energy Magazine - November/December 2015 - 101
IEEE Power & Energy Magazine - November/December 2015 - 102
IEEE Power & Energy Magazine - November/December 2015 - 103
IEEE Power & Energy Magazine - November/December 2015 - 104
IEEE Power & Energy Magazine - November/December 2015 - 105
IEEE Power & Energy Magazine - November/December 2015 - 106
IEEE Power & Energy Magazine - November/December 2015 - 107
IEEE Power & Energy Magazine - November/December 2015 - 108
IEEE Power & Energy Magazine - November/December 2015 - 109
IEEE Power & Energy Magazine - November/December 2015 - 110
IEEE Power & Energy Magazine - November/December 2015 - 111
IEEE Power & Energy Magazine - November/December 2015 - 112
IEEE Power & Energy Magazine - November/December 2015 - Cover3
IEEE Power & Energy Magazine - November/December 2015 - Cover4
https://www.nxtbook.com/nxtbooks/ieee/powerelectronics_september2021
https://www.nxtbook.com/nxtbooks/pes/powerenergy_091021
https://www.nxtbook.com/nxtbooks/pes/powerenergy_070821
https://www.nxtbook.com/nxtbooks/pes/powerenergy_050621
https://www.nxtbook.com/nxtbooks/pes/powerenergy_030421
https://www.nxtbook.com/nxtbooks/pes/powerenergy_010221
https://www.nxtbook.com/nxtbooks/pes/powerenergy_111220
https://www.nxtbook.com/nxtbooks/pes/powerenergy_091020
https://www.nxtbook.com/nxtbooks/pes/powerenergy_070820
https://www.nxtbook.com/nxtbooks/pes/powerenergy_050620
https://www.nxtbook.com/nxtbooks/pes/powerenergy_030420
https://www.nxtbook.com/nxtbooks/pes/powerenergy_010220
https://www.nxtbook.com/nxtbooks/pes/powerenergy_111219
https://www.nxtbook.com/nxtbooks/pes/powerenergy_091019
https://www.nxtbook.com/nxtbooks/pes/powerenergy_070819
https://www.nxtbook.com/nxtbooks/pes/powerenergy_050619
https://www.nxtbook.com/nxtbooks/pes/powerenergy_030419
https://www.nxtbook.com/nxtbooks/pes/powerenergy_010219
https://www.nxtbook.com/nxtbooks/pes/powerenergy_111218
https://www.nxtbook.com/nxtbooks/pes/powerenergy_091018
https://www.nxtbook.com/nxtbooks/pes/powerenergy_070818
https://www.nxtbook.com/nxtbooks/pes/powerenergy_050618
https://www.nxtbook.com/nxtbooks/pes/powerenergy_030418
https://www.nxtbook.com/nxtbooks/pes/powerenergy_010218
https://www.nxtbook.com/nxtbooks/pes/powerenergy_111217
https://www.nxtbook.com/nxtbooks/pes/powerenergy_091017
https://www.nxtbook.com/nxtbooks/pes/powerenergy_070817
https://www.nxtbook.com/nxtbooks/pes/powerenergy_050617
https://www.nxtbook.com/nxtbooks/pes/powerenergy_030417
https://www.nxtbook.com/nxtbooks/pes/powerenergy_010217
https://www.nxtbook.com/nxtbooks/pes/powerenergy_111216
https://www.nxtbook.com/nxtbooks/pes/powerenergy_091016
https://www.nxtbook.com/nxtbooks/pes/powerenergy_070816
https://www.nxtbook.com/nxtbooks/pes/powerenergy_050616
https://www.nxtbook.com/nxtbooks/pes/powerenergy_030416
https://www.nxtbook.com/nxtbooks/pes/powerenergy_010216
https://www.nxtbook.com/nxtbooks/ieee/powerenergy_010216
https://www.nxtbook.com/nxtbooks/pes/powerenergy_111215
https://www.nxtbook.com/nxtbooks/pes/powerenergy_091015
https://www.nxtbook.com/nxtbooks/pes/powerenergy_070815
https://www.nxtbook.com/nxtbooks/pes/powerenergy_050615
https://www.nxtbook.com/nxtbooks/pes/powerenergy_030415
https://www.nxtbook.com/nxtbooks/pes/powerenergy_010215
https://www.nxtbook.com/nxtbooks/pes/powerenergy_111214
https://www.nxtbook.com/nxtbooks/pes/powerenergy_091014
https://www.nxtbook.com/nxtbooks/pes/powerenergy_070814
https://www.nxtbook.com/nxtbooks/pes/powerenergy_050614
https://www.nxtbook.com/nxtbooks/pes/powerenergy_030414
https://www.nxtbook.com/nxtbooks/pes/powerenergy_010214
https://www.nxtbookmedia.com